An airspring can be used in a large vehicle wheel suspension (i.e., a bus or a truck) and/or can be used to manipulate the lift axle of, for example, a large dump truck. In either event, such an airspring commonly comprises a molded body, axial plates to which beads of the molded body are anchored, and a girdle hoop for separating convolutions in the molded body. The molded body comprises rubberized fabric plies having axial end sections wrapped around a circular ring to form the beads of the airspring. The molded body is typically made by building a green preform which is then expanded and shaped by fluid pressure in a heated mold and vulcanized to form the desired shape.
The green preform for the airspring can be built on a mechanical drum. First, multiple plies (i.e., three) of an inner gum liner is assembled on the drum. The fabric plies are then wrapped around the drum to form a cylindrical shape and the bead rings are appropriately aligned with the wrapped fabric plies. End portions of the drum are then radially expanded to seat the bead rings at the correct position relative to the fabric. The end sections of the fabric plies are then turned over the bead rings and the turned end sections are stitched about the beads. After the turn-up is made, cover plies are assembled on the drum to to complete the assembly of the green preform.
Of particular relevance to the present invention is the turn-up device used to turn the end sections of the fabric plies over the bead rings. When a mechanical drum is used to make the green preform, its expandable end portions are each typically comprised of radially movable segments which are separated by slots. The turn-up device has turning components which are inserted into these slots to push the end sections of the fabric plies inwardly and about the bead ring.
The turning device can comprise a sleeve having a series of fingers which are sized and shaped for insertion between the segments in the drum's expandable end portions. (See e.g., U.S. Pat. No. 2,971,562.) The fingers together define a diameter only slightly greater than the diameter of the bead ring and the tolerance of the differential between these diameters has to be substantially tight to insure proper turning. Additionally, with a sleeve as the turning component, longer turn-up lengths cannot be consistently accomplished. Moreover, there is always the potential of the sleeve pushing the bead out of its desired seated position.
To eliminate the bead-unseating problem, an inner sleeve can be positioned within the turning sleeve to hold the bead during the turn-up steps. Such an inner sleeve can comprise a crown-shaped structure having a plurality of fingers aligned with the fingers of the turning sleeve so that it can fit within slots formed by the expanded drum portions. The ends of the fingers of the inner sleeve each have a J-shape recess which together form a cradle for holding the bead during the turn-up steps. When the turn-up device is moved towards the drum, the bead (and the fabric underneath the bead) is received in the recesses and a spring-mounted platform of the inner sleeve contacts the drum. As the turning device continues to move towards the drum, the inner sleeve remains in the same position by compression of its spring mounting and the turning fingers move inward from the inner sleeve to turn the ends of the fabric plies over the bead ring.
While the addition of the bead-holding inner sleeve prevents the bead from moving, it does not help the tight tolerance requirements and, in fact, introduces other tight tolerance issues between the inner sleeve and the outer sleeve and/or between the inner sleeve and the bead. Also, since a sleeve is still the turning component, the length of turn-ups is limited and longer turn-ups can not be consistently accomplished.